The present invention relates to a photocatalytic filter, a photocatalytic filter device to which the photocatalytic filter is applied, and a method for manufacturing a photocatalytic filter.
A photocatalyst is a material that exhibits functions of sterilization, antimicrobial activity, decomposition, deodorization, non-soiling, non-fogging, and the like when exposed to light. When titanium dioxide, a typical example of the photocatalyst, is exposed to light, the titanium dioxide causes an intense redox reaction on its surface to decompose a substance that is in contact with the surface. For example, when the above substance is an organic substance, the organic substance is decomposed into carbon dioxide gas and water. The photocatalyst decomposes, for example, environmental pollutants such as dioxin and trichloroethylene and volatile organic compounds that may cause a sick building syndrome to make them harmless.
Attempts are being made to utilize the above photocatalysis for a filter and apply the filter to disposing of various liquids, disposing of various gases and environmental cleaning.
As a photocatalytic filter that is developed to provide a high-performance photocatalytic filter at a less expensive price, there is proposed a photocatalytic filter using a bundle of photocatalytic filter materials (JP-A-9-225262 and JP-A-10-118415). The above bundle of photocatalytic filter materials is formed by uniformly distributing particles on an outer surface of each of photoconductive filaments (including light transmissive filaments and light guiding filaments), bonding the particles to the outer surface, forming a photocatalyst layer on the outer surfaces of the particles and the remaining outer surface of each filament to produce many photocatalytic filter materials, and bundling these many photocatalytic filter materials such that the forward and backward ends of each photocatalytic filter material are respectively aligned with such ends of other photocatalyst filter materials.
In the above photocatalytic filter, gaps are formed between neighboring photocatalytic filter materials due to the presence of the above particles, so that a fluid to be disposed of is flowed through the gaps to dispose of the fluid.
In the above photocatalytic filter, one end or each end of the bundle of a number of the photocatalytic filter materials is provided with a light incidence portion, and light such as ultraviolet ray is allowed to enter the light incidence portion(s) and propagated inside the photocatalytic filter materials. Since the photocatalyst layers have a higher refractive index (e.g., titanium dioxide; 2.1-2.6) than the filaments (e.g., glass fiber; about 1.5), the above propagated light leaks into the photocatalyst layer without causing total reflection, and the photocatalyst layers are irradiated with the leaked light.
And, a fluid to be disposed of is allowed to flow through gaps formed among the photocatalytic filter materials, and in a state where an organic substance contained in the fluid is in contact with the photocatalyst layers, the photocatalyst layers are irradiated with the above leaked light, so that the organic substance that comes in contact with the photocatalyst layers is decomposed by photocatalysis and removed.
Meanwhile, filaments having numerous particles uniformly distributed on the outer surface thereof are bundled. In this case, the particles that constitute bases for forming gaps are required to have a relatively large diameter for accomplishing the purpose of securing a flow space sufficient for flowing a fluid to be disposed of.
However, linear materials or filaments having a diameter of approximately 70 to 200 μm are preferably used as such, and for bonding numerous particles to outer surfaces of the filaments having such a small diameter, it is desirable to use particles of which the diameter is as small as possible. For example, when one particle is bonded to a surface of a filament having a diameter of 125 μm, properly, the diameter of the particle is approximately 10 μm for securing sufficient adhesion.
When numerous particles having such a very small diameter (approximately 10 μm) are bonded to outer surfaces of the filaments to form a uniform distribution of the particles, it is impossible to overcome the above problem (the requirement to form gaps that secure a sufficient space for flowing a fluid to be disposed of). It is alternatively expected that a spacer having a certain thickness is interposed between one filament and another filament. However, it is impossible to interpose such a spacer among the filaments having a very small diameter in essence.
A photocatalytic filter is conventionally required to secure gaps formed among photocatalytic filter materials that are bundled, as a flow space for flowing a fluid to be disposed of. However, no conventional photocatalytic filters can comply with the above requirement. Further, it is conventionally required to form a gap structure suitable for trapping an organic substance of the fluid that is brought into contact with a photocatalyst layer. Again, however, no conventional photocatalytic filters can comply with the above requirement.
A conventional photocatalytic filter is constituted of a number of photocatalytic filter materials that are bundled, and it is conventionally required to develop a method having improved productivity in the step of bonding particles to filter materials. However, such a method has not yet been developed.